1. Field of the Invention
This invention relates in general to a method for determining the relationship between the original bulk volume of oil, effective porosity and height above the oil-water contact level for a well penetrating a reservoir. A first embodiment of the invention relates to a method for determining and recording as a function of depth, the original bulk volume of oil and saturations of a produced well using core data, and where an original porosity log does not exist, combining information from an original resistivity log to determine and record original bulk volume of oil and saturation. According to an alternative embodiment of the invention, well logs of a well are used exclusively to determine such relationship for the case where the well penetrates the oil-water contact level. According to another alternative embodiment of the invention where a well does not penetrate the oil-water contact level, core data and well log data are used to determine the depth of the oil-water contact level.
2. Description of the Prior Art
A paper by G. M. Heseldin entitled "A Method of Averaging Capillary Pressure Curves" published in the SPWLA Fifteenth Annual Logging Symposium, June 2-5, 1974 describes a method for determining an average capillary pressure curve for a particular rock type. Heseldin describes how capillary pressure data from a number of core samples of a zone of the formation can be plotted with constant capillary curves on an x-y grid where total effective porosity .phi..sub.E is measured on the y ordinate and bulk volume of oil, or .phi..sub.o is plotted on the x - abscissa. Heseldin describes a method of characterizing any curve as a displaced rectangular hyperbola of the form, EQU (.phi..sub.E -A).sup.2 =(.phi..sub.o).sup.2 +B.sup.2,
and then shows that the constants A and B are essentially linear with the logarithm of capillary pressure P.sub.c.
A disadvantage of the Heseldin approach is that no single relationship is established by which the bulk volume of oil .phi..sub.o may be expressed as a function of effective porosity and capillary pressure P.sub.c.